As for basic duplex modes adopted by a cellular system, a TDD (Time division duplex) mode refers to the situation that an uplink and a downlink use a same working frequency band, uplink and downlink signals are transmitted at different time intervals and a Guard Period (GP) exists between the uplink and the downlink; and an FDD (Frequency division duplex) mode refers to the situation that the uplink and the downlink use different working frequency bands, uplink and downlink signals can be transmitted on different frequency carriers at the same time and a Guard Band (GB) exists between the uplink and the downlink.
A frame structure of an LTE (Long Term Evolution) TDD system is slightly complex. As shown in FIG. 1A, the length of a radio frame is 10 ms, the radio frame contains two types of subframes. i.e. special subframes and normal subframes, the number of which is 10 in total, and the length of each subframe is 1 ms. The special subframes are divided into three subframes: a DwPTS (Downlink Pilot Time Slot) used for transmitting a PSS (Primary Synchronization Signal), a PDCCH (Physical Downlink Control Channel), a PHICH (Physical HARQ Indication Channel), a PCFICH (Physical Control Format Indication Channel), a PDSCH (Physical Downlink Shared Channel) and the like; a GP used as the Guard Period between the downlink and the uplink; and an UpPTS (Uplink Pilot Time Slot) used for transmitting an SRS (Sounding Reference Signal), a PRACH (Physical Random Access Channel) and the like. The normal subframe includes uplink subframes and downlink subframes which are used for transmitting uplink/downlink control channels, traffic data and the like. One radio frame can be configured with two special subframes (positioned at the subframes 1 and 6), or can be configured with one special subframe (positioned at the subframe 1). The subframe 0 and the subframe 5, as well as the DwPTS in the special subframes, are always used for downlink transmission; the subframe 2 and the UpPTS in the special subframes are always used for uplink transmission; and other subframes can be configured for uplink transmission or downlink transmission as required.
In the TDD system, the uplink transmission and the downlink transmission use the same frequency resources and uplink/downlink signals are transmitted on the different subframes. The common TDD system including a 3G TD-SCDMA (Time Division Synchronous Code Division Multiple Access) system and a 4G TD-LTE system, the uplink and downlink subframes are partitioned statically or semi-statically and it is common to determine the proportional partition of the uplink and downlink subframes during a network planning according to the type of a cell and the approximate traffic proportion and keep the proportional partition unchanged. This is a relatively simple and effective scheme under the background of large coverage of macro cells. However, with the development of technologies, more and more Pico cells, Home NodeBs and other low-power base stations are deployed to provide local small coverage. There are a smaller number of User Equipments (UEs) and a significant change in UE's traffic requirements in these cells, thus the configuration of uplink sub-frames and downlink sub-frames is needed to be varied dynamically.
In an actual system, if different uplink and downlink subframe configurations are set for different cells, cross link interference of the adjacent cells can be caused. As shown in FIG. 1B, a femto cell is configured to receive the uplink signals on a time slot on which the macro cell transmits the downlink signals, then base station-base station interference occurs between the two cells and a femto base station directly receives the downlink signals from a Macro base station, so that the quality of L-UE (Local UE) uplink signals received by the femto base station is seriously affected.
The adjacent cells herein can be the geographically adjacent cells using a same TDD carrier (as shown in FIG. 1B), or the geographically overlapped cells or the cells using adjacent TDD carriers (as shown in FIG. 1C). Simultaneously, the adjacent cells herein can be the cells deployed at the same layer (such as the macro cells) or the cells deployed in layers (such as the macro cells, the Pico cells, the Home NodeBs and the like).
As reconfigurations of the uplink and the downlink of a TDD cell are relatively flexible, cross link interference strength is increased. However, there is no solution for reducing the cross link interference in TDD networking at present.